1. Field of the Invention
The present invention relates to an image pickup information output apparatus adapted to output image pickup information on an image pickup system which includes a lens apparatus and an image pickup apparatus, and more particularly, to an image pickup information output apparatus adapted to output image pickup information that the lens apparatus has, in the image pickup system which includes the lens apparatus and image pickup apparatus, as well as to the lens apparatus equipped with the image pickup information output apparatus.
2. Description of the Related Art
Conventionally, an image pickup information output apparatus adapted to calculate and display object distance information, focal length information, an f-number, depth of field and an angle of view which are image pickup conditions of a camera is disclosed in Japanese Utility Model Application Laid-Open No. H01-78464, where the image pickup conditions are calculated from focus lens position, zoom lens position and stop position. Also, a three-dimensional image pickup apparatus is known which varies an optical axis angle (referred to as a convergence angle) between left and right lenses during three-dimensional photography, and thereby adjusts a three-dimensional effect of three-dimensional video. In this case, a display control apparatus which calculates and records the convergence angle or a convergence distance based on shift lens position and zoom lens position is disclosed in Japanese Patent Application Laid-Open No. 2011-135604, where the convergence distance is a distance from an image pickup apparatus to a point of intersection between the optical axes of the left and right lenses and the shift lens is used for adjustment of the optical axes.
Japanese Patent Application Laid-Open No. S63-182620 discloses a technique for automatically correcting a deviation of a focusing position by driving a focus lens according to changes in focal length, the focus lens being a varifocal lens which varies focus lens position depending on zoom lens position even when an object distance, which is an image pickup condition, is constant.
Japanese Patent Application Laid-Open No. H07-306356 discloses a technique for displaying an object distance by calculating the object distance from zoom lens position and an operating range of a focus lens, where the focus lens is a varifocal lens which varies focus lens position depending on the zoom lens position even when the object distance, which is an image pickup condition, is constant.
It becomes sometimes necessary to output image pickup conditions of an image pickup lens, such as the object distance, f-number, focal length, depth of field, angle of view, convergence distance at a given time point to the outside such as to an image pickup operator. Since it is necessary to output information about an actual state in which image pickup is performed, when information about the image pickup conditions are acquired from a state of a lens apparatus itself, the image pickup conditions need to be computed and found from positions of plural optical members including the focus lens, zoom lens, stop, and shift lens. Furthermore, these optical members vary with plural image pickup conditions. This involves trouble because even if the image pickup conditions set by the operator is not changed, if a setting of another image pickup condition is changed, image pickup condition information will change. To deal with this, a lens control apparatus is disclosed which makes automatic corrections such that even if an image pickup condition changes, other image pickup conditions will not be affected. However, there can arise a problem in that image pickup condition information will change due to calculation errors in image pickup condition information even if image pickup conditions are fixed during an automatic correction process if changes occur in position detection accuracy errors as a result of synchronization delays among plural optical members or changes in travel ranges of the optical members.
For example, the above problem will be described concretely by taking as an example the object distance of a varifocal lens. With a varifocal lens, position of the focus lens with respect to a predetermined object distance is a function of zoom lens position, and thus the object distance can be found from the focus lens position and zoom lens position. Therefore, in setting an object distance, a targeted focus lens position is determined from the set object distance and zoom lens position. Furthermore, since the zoom lens position changes during the setting of focal length, in order to keep the object distance constant, the focus lens position needs to be adjusted automatically according to the zoom lens position. Automatic object distance adjustment such as described above is disclosed in Japanese Patent Application Laid-Open No. S63-182620.
Furthermore, an object distance display apparatus for a varifocal lens is disclosed in Japanese Patent Application Laid-Open No. H07-306356, where the display apparatus calculates and displays an object distance based on zoom lens position and focus lens position.
Consequently, even if the focal length changes, the object distance can be displayed by maintaining a set object distance.
However, since the focus lens is driven and the object distance is calculated according to zoom lens position, if there is a delay in driving the focus lens with respect to variations in zoom lens position, the focus lens cannot be moved in an instant to the focus lens position corresponding to targeted object distance in response to a change in the focal length, and consequently, the object distance calculated from the zoom lens position and focus lens position deviates by the amount corresponding to the delay in following the change in the focal length. Furthermore, the travel range of the focus lens from infinity to the closest range varies between when the zoom lens position is on a wide-angle side and when the zoom lens position is on a telephoto side while position detection accuracy remains constant even when the focus lens moves, and consequently, the accuracy of object distance corresponding to the focus lens position varies with the focal length. Therefore, since the accuracy of object distance varies with the focal length even if the object distance is the same, the object distance changes even if the automatic object distance adjustment described above is carried out according to the focal length. The change in the object distance may cause the photographer to misunderstand that the lens is malfunctioning. The same is similarly true for the f-number, focal length, depth of field, angle of view, convergence distance in addition to the object distance.
The conventional techniques disclosed in the patent documents described above do not describe how to deal with changes in object distance caused by synchronization errors of the lens or lens position detection accuracy.